1. Field of the Invention
This invention relates generally to ink jet paper used in ink jet printing and, more particularly, to a coating composition suitable for making matte grade coated ink jet paper. The improvement relates to the use of a paper coating composition primarily of an engineered kaolin clay which is treated with a cationic polymer.
2. Description of Related Art
In ink jet printing, uniformly shaped droplets of aqueous or solvent-based dye solutions are ejected from a nozzle onto a paper or other substrate. The paper and surface chemistry requirements for good print quality vary widely and may rely on coating materials to create appropriate ink sorption characteristics.
Ink jet inks may be water-based or may have an alkylene glycol or other solvent base.
For the printing of well shaped dots by means of ink jets, and especially for multi-color printing with ink jets, the use of paper coated with a pigment is highly desirable. The pigment and the binder of the coating may generally serve to sorb the solvent of the ink (i.e. dry the ink) and hold the dye stuff of the ink on the surface of the coating to maximize the visual effect of the ink.
A binder used in a paper coating generally serves the function of holding the pigment so as to reduce or eliminate dusting or chalking thereof, since ink jet printers with very fine orifice nozzles are quite susceptible to clogging. Also, the binder should help in the sorption of the solvent of the ink. If too high a binder is used, ink will remain on the surface and will smear or even splatter when hitting the surface after ejection from the nozzle. Too weak a binder will not hold the pigment without chalking.
U.S. Pat. No. 4,892,787 issuing on Jan. 9, 1990 discloses a cellulosic substrate coated with a mixture of a particular pigment having a surface range of about 100 to 350 m.sup.2 /g and an average particle size of less than about 8 .mu.m, and a binder comprising a mixture of an acrylic resin and polyvinyl alcohol in effective amounts to minimize chalking of the pigment and to sorb solvent from the water-or glycol-based jet printing ink. The pigment is selected from the group consisting of silica, alumina, silica-aluminum and titania.
The teachings of this U.S. Pat. No. 4,892,787 provide a coating with fractal dimension of less than 1.1 and aspect ratios of less than 1.1, as exhibited by dots formed by ink jet printers on the coating disclosed therein. The coating does not chalk, but other printing performance factors of the ink jet paper, such as color ink densities, ink drying rate, water fastness resistance, wicking and bleeding are not addressed in this U.S. Pat. No. 4,892,787.
U.S. Pat. No. 5,281,467 issuing on Jan. 25, 1994 discloses an ink jet recording paper with a coating containing a pigment which achieves excellent ink absorption, smoothness, gloss, and water resistance together with an excellent dot density, sharpness, and roundness to ensure recording of high quality, high contrast full color images. The coating is applied to a support by a cast coating method, and the pigment comprises at least 50 weight percent of a calcium carbonate-compounded silica. The average particle size of the compound silica is no greater than 3 .mu.m in order to increase dot sharpness and density. The specific surface area of the compound silica as measured by the BET method is preferably no greater than 80 m.sup.2 /g. A binder is added to the coating composition in order to improve adhesion of the pigment to the support and render the coating uniform. It is also desirable that the coating contain a cationic polymer to improve the water resistance of the recorded image. Some disadvantages of the coating of this U.S. Pat. No. 5,281,467 is that the coating composition in slurry form contains low coating solids, poor rheology, and is expensive to manufacture.
U.S. Pat. No. 4,554,181 issuing on Nov. 19, 1985 to the Mead Corporation discloses an ink jet recording sheet having a recording surface which includes a combination of a water soluble polyvalent metal salt and a cationic polymer having cationic groups which are available in the recording surface for insolubilizing an anionic dye. The recording surface may be formed by applying an aqueous solution of the aforesaid salt and polymer to the surface of an absorbent sheet material such as paper or by applying a coating containing the polymer and salt combination alone or in combination with a binder which may be water swellable, and other additives, to the surface of a substrate, such as paper or plastic film. The combination of the salt and cationic polymer achieve images of improved density, water fastness, and sharpness. Coated paper products can be prepared by incorporating a water soluble polyvalent metal salt and a cationic polymer or latex into a conventional paper coating composition and applying the coating to the paper substrate using conventional coating techniques. Such conventional coatings typically include a white pigment such as clay, diatomaceous earth, baryta, and/or calcium carbonate, and a binder such as gelatin, etherified starch, or polyvinyl alcohol.
U.S. Pat. No. 4,425,405 to Mjrakami et al. describes a coating composition containing a white filler and polyvinyl pyrrolidone. Preferably, the salt and the cationic polymer are added to this coating composition in an amount of about 0.1 to 30 parts per 100 parts composition.
U.S. Pat. No. 5,270,103 to Oliver et al. discloses the use of coated ink jet sheets comprising a silicate or silicate pigment with a two component binder of polyvinyl alcohol and cationic polymers, including polyamines, to improve color density.
The prior art, including that described hereinabove, disclose specific means and/or methods for achieving certain objectives, such as high image quality, such as high color sharpness and high resolution or high printing performance, such as reduced offset, feathering, paper curl, and improved water fastness, and the prior art has several drawbacks and disadvantages. In some of the teachings of the prior art, the density, sharpness, and roundness of each dot still may not be good enough to obtain high quality, high contrast, full color recorded images for ink jet paper.
Some coating compositions, such as silica-based coatings, applied to a substrate, tend to produce an ink jet paper with a relatively high print performance. However, the costs for these commercially available papers with silica coatings tend to be high due to the raw materials and the manufacturing process.
It would be ideal to have commercially available, an ink jet paper with at least the same or better quality print performance as those with the silica-based coating compositions, but produced at a lower manufacturing cost and at higher coat weights to increase opacity for two-sided printing.